In semiconductor device fabrication processes, colloidal silica type abrasives have commonly been studied as chemomechanical abrasives for smoothing inorganic insulating film layers such as SiO.sub.2 insulating films formed by a process such as plasma-assisted CVD (chemical vapor deposition) or low-pressure CVD. Colloidal silica type abrasives are produced by growing silica particles into grains by, e.g., thermal decomposition of silicon tetrachloride, followed by pH-adjustment with an alkali solution containing non alkali metal, such as aqueous ammonia. Such abrasives, however, have a technical problem of a low polishing rate which prevents them being put into practical use, because the inorganic insulating films can not be polished at a sufficiently high polishing rate.
Meanwhile, cerium oxide abrasives are used in glass-surface polishing for photomasks. The cerium oxide abrasives are useful for finish mirror polishing because they have a hardness lower than silica particles and alumina particles and hence the polishing surface is very difficult to scratch. Also, cerium oxide has a chemically active nature and is known as a strong oxidizing agent. Making the most of this advantage, it is useful to apply the cerium oxide in chemomechanical abrasives for insulating films. However, if the cerium oxide abrasives used in glass-surface polishing for photomasks are used in the polishing of inorganic insulating films as they are, they have so large a primary particle diameter that the insulating film surface may come to have polish scratches which are visually perceivable.